UBL-SR-21
Error (blocking) EN 16931 (UBL)
Official rule text
Payee legal registration identifier shall occur maximum once, if the Payee is different from the Seller
Seeing UBL-SR-21 in a rejection?
Run your file through the free validator to see every violation at once — or let NormDrift watch your reference invoices so the next ruleset release never surprises you.